1. Field of the Invention
This invention relates generally to a tone arm assembly for a record player and, more particularly is directed to a novel apparatus for such a tone arm assembly, whereby the horizontal movement and also the vertical movement are controlled servo-controlled motors.
2. Description of the Prior Art
A control apparatus for a tone arm assembly is known that uses one or more motors to move a tone arm in the horizontal and vertical directions relative to the surface of a record disc. For example, such apparatus includes a horizontal drive motor for moving the tone arm from its so called rest position to a playing position disposed above the record disc during a lead-in operation and for returning the tone arm back to its rest position during a lead-out operation after completing a reproducing or playing operation of the record. Such apparatus also includes a vertical drive motor for moving the tone arm in the vertical direction, that is, for lowering the tone arm onto the record disc and for lifting the tone arm therefrom. It is desirable, in such apparatus for the tone arm to move at a constant velocity from its rest position to a record reproducing position or from a record playing final position to its rest position. To this end, there is provided a so-called constant velocity servo circuit such that the moving or actual velocity of the tone arm is detected and this detected output is used to control the motor to maintain constant velocity. One type of velocity detector which has been proposed for a constant velocity servo circuit includes the combination of a slit plate movable with the motor or tone arm and having a plurality of slits therein and a light emitting element and a light sensing element, the latter elements being positioned with the slit plate interposed therebetween, as described in U.S. Ser. No. 923,455 assigned to the assignee of this invention. This optical detecting device is arranged to operate by producing pulse signals whose widths are a function of the tone arm velocity and detecting the widths of these pulses. The servo circuit operates to increase the motor velocity when the pulse widths become wide and to decrease the motor velocity when the pulse widths become narrow. Such detecting device and servo circuit, however, have a mechanical-electrical converter and a circuit for accurately detecting pulse widths, so that the construction of such apparatus is relatively complicated. Further, since the drive motor and the detecting device generally are unbalanced in weight, if they are mounted on, for example, the drive shaft for the tone arm, there is a possibility that such use, over a prolonged period of time, may result in undesired transformation of the bearing of the tone arm.
In a tone arm control apparatus, the completion of the record-playing operation must be sensed to initiate a lead-out operation. This is generally accomplished by detecting the horizontal velocity of the tone arm which is increased when the tone arm tracks the final spiral groove of the record disc. This tone arm velocity sensing operation is performed by a velocity detector which typically is separate from the servo circuit velocity detector, with the result that the overall construction becomes even further complicated.